It uses Math.min and Math.max in a very tight loop. I think we could apply point #9 here

I just checked the nightly build. I see that the CompositeSprite.getBBox method can skip sprites from bbox calculations when the sprite has the bboxExcluded (true) attribute. This is a very simple an effective feature. I hope this is not just for internal use. I have a large number of sprites that can be excluded, so this should speed up bbox calculations.